The present invention relates to antenna arrays, and more particularly, to a common aperture dual polarization array that employes a flat plate shunt slot standing wave array and a short backfire array that are fed by a centered collinear standing wave array.
Advanced seekers require high performance antennas for radiating electromagnetic energy containing horizontal and Vertical polarization components. There are a variety of dual-polarization seeker antenna arrays presently known upon which the present invention improves. These include a reflector antenna array employing a dual polarization feed. The reflector antenna array is bulky and its efficiency is low. Furthermore, it is very difficult to achieve low sidelobe array pattern in the reflector antenna array.
A second antenna array is a patch antenna array. The patch antenna array is low cost and low profile, but the bandwidth of each of its elements is extremely narrow. Therefore, producing a high performance antenna array using the patch element antennas is very difficult. Also, the efficiency of the patch antenna array is poor.
A third antenna array is a combination antenna array that is comprised of a shunt slot array fed by a rectangular waveguide that provides for vertical polarization, and a dipole array fed by a stripline that provides for horizontal polarization. This combination antenna array employs an efficient vertical polarization array, but the dipole array fed by the stripline is bulky. More particularly, control of the input impedance seen at the stripline of each dipole that is required to achieve a low sidelobe pattern is very difficult to achieve, and the overall input match of the array is also very difficult to achieve. The phase matching between the vertical polarization array and the horizontal polarization array is difficult because each array uses a different transmission line.
A fourth antenna array is a fully populated dual polarization standing wave array fed by a waveguide. This antenna array is described in copending U.S. patent application Ser. No. 08/470,528, filed Jun. 6, 1995 now U.S. Pat. No. 5,543,810, entitled "Common Aperture Dual Polarization Array Fed By Rectangular Waveguides", and is assigned to the assignee of the present invention. This antenna array is very complex for the case where the required gain of the horizontal polarization array is slightly greater than the gain of one quadrant of the main vertical polarization array. Such complexity results in a very costly and difficult to produce antenna array.
Consequently, it is an objective of the present invention to provide for a common aperture dual polarization array that improves upon the above-mentioned antenna arrays. It is a further objective of the present invention to provide for a common aperture dual polarization array that employs a flat plate shunt slot standing wave array and a short backfire antenna array that are fed by a centered collinear standing wave antenna array.